Catalysts of the double-metal cyanide complex class, such as zinc cobalticyanide, are well known. Methods for making these catalysts and of using them to make polyalkylene ethers or oxides by the polymerization of alkylene oxides are disclosed in U.S. Pat. Nos. 3,278,457; 3,278,458 and 3,278,459 and divisions thereof Nos. 3,427,256; 3,427,334 and 3,427,335. Methods for making polyalkyleneether polyols using these double metal cyanide catalysts, also, are known as shown by U.S. Pat. Nos. 3,829,505 and 3,941,849 (a division).
The process of U.S. Pat. No. 3,829,505 desirably produces polyalkyleneether polyols which exhibit higher molecular weights, higher hydroxyl functionality and lower unsaturation at the desired higher functionality and molecular weight levels than polyalkylene ether polyols produced by the use of conventional alkaline catalysts. These polyols, also, can be made with low or high molecular weights and with low or high hydroxyl functionality so that they can be used in the manufacture of flexible to rigid polyurethane foams, rubbers, thermoplastics and thermosets. Polyether polyols made with alkaline catalysts have limiting molecular weights. For example, a feature of the use of the double metal cyanide catalyst is the ability to get high molecular weight polypropylene ether triols in contrast to the limiting value of about 6,000 when alkali catalysts are used. In other words the use of alkali catalysts to produce high molecular weight, hydroxyl terminated, polypropylene ethers results in a substantial loss in hydroxyl functionality, while when using the double metal cyanide catalyst, one is able to obtain near theoretical hydroxyl functionality (i.e. 3, if a triol is used as initiator for the PO polymerization) at even very high molecular weights.
However, it has been found that the double metal cyanide complex catalyst residues present in such polyols after polymerization cause certain undesirable reactions both prior to and during their use in making polyurethane products. For example, it has been found that such polyols, e.g., polypropylene ether polyols, containing the double metal cyanide complex catalyst residues, are less stable during storage and tend to build up volatile impurities at a faster rate than polyols devoid of the catalyst residues. These volatiles may give an odor to the polyol and may be acetaldehyde, acetone, propionaldehyde and/or propylene oxide.
Also, it has been found that such catalyst residues in the polyol catalyze the formation of a significant amount of allophanate groups during reaction of the polyol and the polyisocyanate. The formation of such allophanate groups gives a product which is cross linked or chain branched but less stable to heat and, in the case of prepolymers, gives a product which exhibits increased viscosity. Interestingly, certain zinc and cobalt carboxylates are in many cases catalysts of allophanate formation (I. C. Kogon, J. Org. Chem. 26, 3004 (1961)). Moreover, chain branching may affect viscosities. The allophanates are, apparently, intermolecularly hydrogen bonded (I. C. Kogon, J. Am. Chem. Soc. 79, 2253 (1957)). Allophanates, also, are more highly polar then urethanes.
Additionally, it is well known that it is most desirable to make polyurethanes from polyols containing primary hydroxyl groups. Primary hydroxyl groups react faster than secondary hydroxyl groups. Even when mixtures of ethylene oxide and propylene oxide are copolymerized together using the double metal cyanide complex catalyst, the end groups are principally secondary hydroxyl groups since ethylene oxide reacts faster than propylene oxide. In such copolymerizable mixtures, ethylene oxide is used in a minor molar amount, usually not over about 30 mol %, of the total alkylene oxide monomer mixture to prevent water sensitivity. Primary hydroxyl terminated polyols are desired since polyurethane products can be prepared from primary hydroxyl terminated polyols under less severe conditions than when they are prepared using polyols terminated with secondary hydroxyl groups.
Moreover, it was found that when ethylene oxide was added to a polyetherpolyol such as polypropylene ether polyol made with a double metal cyanide catalyst and containing residues of such catalyst, some addition of ethylene oxide to the polyol did take place. However, the major reaction was the homopolymerization of ethylene oxide. This resulted in a heterogenous mixture of crystalline poly (ethylene ether) polyol and poly (propylene ether) polyol which gave unsatisfactory products on reaction with polyisocyanates.
Accordingly, it is an object of the present invention to provide a method or process for treating polyalkylene ether polyols containing double metal cyanide complex catalyst residues to remove said residues and provide polyalkylene ether polyols with a reduced tendency to form allophanate groups.
Another object of this invention is to provide a method for treating polyalkylene ether polyols containing double metal cyanide complex catalyst residues to remove said catalyst residues and to end cap said polyols with ethylene oxide to provide said polyols with primary hydroxyl end groups.
These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description and working examples.